Week 1, Lecture 3

The Human Tissues

Reference Book:

Anatomy & PhysiologyThe Unity Of Form And Function

Ninth Edition;Kenneth S. Saladin

Lecture delivered by

Dr Vini Gautam

Lecturer

Department of Biomedical Engineering

Lecture Outline

Kinds of tissues in human body:

Epithelial tissue

Connective tissue

Nervous and Muscular (excitable) tissue

Tissue growth

Tissue development

Stem cells

Tissue repair and degeneration

Clinical application: stem cell therapy and regenerative medicine

My own research

Introduction

50 trillion (1012) cells of 200 different cell types

Cells > tissues > organs

Tissue = group of similar cells working together toperform a specific role in an organ
Organ = structure with discrete boundaries that iscomposed of two or more tissue types
Four broad categories of tissues:

Epithelial tissue
Connective tissue
Nervous tissue
Muscular tissue

The Primary Tissue Classes

The four primary tissues (epithelial, connective, nervous,and muscular) differ from each other in:

Types and functions of their cells
Characteristics of the matrix (extracellular material)
Relative amount of space occupied by cells versus matrix

Matrix (extracellular material) is composed of:

Fibrous proteins
Clear gel called ground substance

Also known as tissue fluid, extracellular fluid (ECF), interstitial fluid, or tissue gel

Epithelial Tissue

(a) Light microscope view of the nonkeratinized stratified squamous epithelium of the vaginal lining.

(a) The classes of epithelia are simple, stratified and pseudostratified.
(b) Cell shapes are squamous, cuboidal, and columnar.

Epithelia aresheets of closely adhering cells, one or more cells thick

Epithelial Tissue1

Covers body surfaces and lines body cavities
Upper surface usually exposed to the environment or an internal spacein the body
Constitutes most glands
Avascular (does not have blood vessels)

Usually nourished by underlying connective tissue

Epithelial Tissue2

Functions:

Protect deeper tissues from injury and infection
Produce and release chemical secretions
Excrete wastes
Absorb chemicals including nutrients
Selectively filter substances
Sense stimuli

Epithelial Tissue3

Epithelial cells are very close together
Have a high rate of mitosis
Basement membrane—layer between an epithelium andunderlying connective tissue

Collagen, reticular proteins, glycoproteins, other protein–carbohydrate complexes
Anchors the epithelium to the connective tissue below it

Epithelial Tissue4

Simple epithelia

Contain one layer of cells
Named by shape of cells
All cells touch basement membrane

Stratified epithelia

Contain more than one layer
Named by shape of apical cells
Some cells rest on top of others and do not touchbasement membrane

Simple Squamous Epithelium

(a) Light microscope view of the single layer of squamous epithelial cells comprising the serosa of the small intestine.

Simple squamous epithelium

Single row of thin cells
Permits rapid diffusion or transport of substances
Secretes serous fluid
Locations: alveoli, glomeruli, endothelium,andserosa

Figure 5.4

Access the text alternative for slide images.

a:DennisStrete/McGraw-Hill Education

Simple Cuboidal Epithelium

(a) Light microscope view of the single layer of cuboidal cells lining the kidney tubules.

Simple cuboidal epithelium

Single layer of square or round cells
Absorption and secretion, mucus production andmovement
Locations: liver, thyroid, mammary and salivaryglands,bronchioles, and kidney tubules

Figure 5.5

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a:DennisStrete/McGraw-Hill Education

Simple Columnar Epithelium

(a) Light microscope view of the single layer of columnar cells lining the inside surface of the small intestines.

Simple columnar epithelium

Single row of tall, narrow cells
Oval nuclei in basal half of cell
Brush border of microvilli, ciliated in some organs, maypossess goblet cells
Absorption and secretion; secretion of mucus
Locations: lining of GI tract, uterus, kidney, and uterinetubes

Figure 5.6

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a:Ed Reschke/Getty Images

Pseudostratified Epithelium

(a) Light microscope view of the ciliated pseudostratified columnar epithelium lining the inside surface of the trachea.

Pseudostratified epithelium

Looks multilayered, but all cells touch basement membrane
Nuclei at several layers
Has cilia and goblet cells
Secretes and propels mucus
Locations: respiratory tract and portions of male urethra

Figure 5.7

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a:DennisStrete/McGraw-Hill Education

Keratinized Stratified Squamous Epithelium

Keratinized stratified squamous

Multiple cell layers; cells become flat and scaly towardsurface
Resists abrasion; retards water loss through skin; resistspenetration by pathogenic organisms
Locations: epidermis; palms and soles heavilykeratinized

Figure 5.8

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a:©Ed Reschke

Non-keratinized Stratified Squamous Epithelium

Nonkeratinized stratified squamous

Same as keratinized epithelium without surface layer ofdead cells
Resists abrasion and penetration of pathogens
Locations: tongue, oral mucosa, esophagus, and vagina

Figure 5.9

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a:©Ed Reschke

Stratified Cuboidal Epithelium

Stratified cuboidal epithelium

Two or more cell layers; surface cells square or round
Secretes sweat; produces sperm, produces ovarianhormones
Locations: sweat gland ducts; ovarian follicles andseminiferous tubules

Figure 5.10

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a:Lester V. Bergman/Corbis NX/Getty Images

Connective Tissue

A diverse type of tissue in whichcells occupy less space than matrix

(a) Light microscope view of fibrocartilage.
(b) Drawing of fibrocartilage.

(a) Light microscope view of a blood peripheral smear.
(b) Drawing of a blood peripheral smear.

Connective Tissue: Overview1

Most cells are not in direct contact with each other
Supports, connects, and protects organs
Highly variable vascularity

Loose connective tissues have many blood vessels
Cartilage has few or no blood vessels

Connective Tissue: Overview2

Functions of connective tissues:

Connecting organs—tendons and ligaments
Support—bones and cartilage
Physical protection—cranium, ribs, sternum
Immune protection—white blood cells attack foreigninvaders
Movement—bones provide lever system
Storage—fat, calcium, phosphorus
Heat production—metabolism of brown fat in infants
Transport—blood

Fibrous Connective Tissue2

Fibers of fibrous connective tissue:

Collagenous fibers

Collagen is most abundant of the body’s proteins—25%
Tough, flexible, and stretch-resistant
Tendons, ligaments, and deep layer of the skin are mostly collagen; itis less visible in the matrix of cartilage and bone

Reticular fibers

Thin collagen fibers coated with glycoprotein
Form framework of spleen and lymph nodes

Elastic fibers

Thinner than collagenous fibers, made of protein elastin
Allows stretch and recoil

Areolar Tissue

(a) Light microscope view of areolar connective tissue in a spread of the mesentery.
(b) Drawing of areolar connective tissue in a spread of the mesentery.

Areolar tissue

Loosely organized fibers, abundant blood vessels
Underlies epithelia, in serous membranes, betweenmuscles, passageways for nerves and blood vessels

Reticular Tissue

(a) Light microscope view of reticular connective tissue in the spleen.
(b) Drawing of reticular connective tissue in the spleen.

Reticular tissue

Mesh of reticular fibers and fibroblasts
Forms supportive stroma (framework) for lymphaticorgans
Found in lymph nodes, spleen, thymus, and bonemarrow

Dense Regular Connective Tissue

Dense regular connective tissue

Densely packed, parallel collagen fibers
Compressed fibroblast nuclei
Elastic tissue forms wavy sheets in some locations
Tendons attach muscles to bones and ligamentsholdbones together

Figure 5.16

Dense Irregular Connective Tissue

Dense irregular connective tissue

Densely packed, randomly arranged, collagen fibersand few visible cells
Withstands unpredictable stresses
Locations: deeper layer of skin; capsules aroundorgans

Figure 5.17

Adipose Tissue

Adipose tissue (fat)—tissue in which adipocytes are thedominant cell type
Space between adipocytes is occupied by areolar tissue,reticular tissue, and blood capillaries
Fat is the body’s primary energy reservoir

The quantity of stored triglyceride and the number ofadipocytes are quite stable in a person
Fat is recycled continuously

New triglycerides synthesized while old molecules hydrolyzed andreleased to blood

Adipose Tissue

Adipose tissue

Empty-looking cells with thin margins; nucleuspressed against cell membrane
Energy storage, insulation, cushioning

Subcutaneous fat and organ packing
Brown fat of juveniles produces heat

a:DennisStrete/McGraw-Hill Education

Cartilage1

Stiff connective tissue with flexible matrix

Gives shape to ear, tip of nose, and larynx

Chondroblasts—cartilage cells that produce the matrix thatwill trap them

Chondrocytes—cartilage cells that are trapped in lacunae(cavities)

Perichondrium—sheath of dense irregular connective tissuethat surrounds elastic and most hyaline cartilage (notarticular cartilage)

Contains a reserve population of chondroblasts thatcontribute to cartilage growth throughout life

Cartilage2

No blood vessels (avascular)

Diffusion brings nutrients and removes wastes
Heals slowly

Matrix rich in GAGs and contains collagen fibers

Types of cartilage vary with fiber composition

Hyaline cartilage, fibrocartilage, and elastic cartilage

Hyaline Cartilage

Hyaline cartilage

Clear, glassy appearance because of fineness of collagen fibers
Eases joint movement, holds airway open, moves vocal cords,growth of juvenile long bones
Locations: articular cartilage, costal cartilage, trachea, larynx, fetalskeleton

a:©Ed Reschke

Elastic Cartilage

Elastic cartilage

Cartilage containing abundanceof elastic fibers
Covered with perichondrium
Provides flexible, elastic support
Locations: external ear andepiglottis

a:©Ed Reschke

Fibrocartilage

Cartilage containing large, coarse bundles of collagen fibers
Resists compression and absorbs shock
Locations: pubic symphysis, menisci, and intervertebral discs

a:Dr.AlvinTelser

Bone1

Bone (osseous) tissue is acalcifiedconnective tissue

Two forms of osseous tissue:

Spongy bone: porous appearance

Delicate struts of bone: trabeculae
Covered by compact bone
Found in heads of long bones and in middle of flat bones such asthe sternum

Compact bone: denser, calcified tissue with no visiblespaces

More complex arrangement
Cells and matrix surround vertically oriented blood vessels in longbones

Compact Bone

Compact bone is arranged in cylinders that surround central(osteonic) canals that run longitudinally through shafts oflong bones

Blood vessels and nerves travel through central canal

Bone matrix deposited in concentric lamellae

a:DennisStrete/McGraw-Hill Education

Blood

Fluid connective tissue
Transports cells and dissolved matter from place to place
Plasma—blood’s ground substance (matrix)

Erythrocytes—red blood cells (RBCs): transport O2andCO2
Leukocytes—white blood cells (WBCs): defend againstinfection and disease

Neutrophils, eosinophils, basophils, lymphocytes, monocytes

Platelets—cell fragments involved in clotting

Excitable tissues

Ability to respond to stimuli bychanging membrane potential

E.g. nerve cells, muscles

(b) Drawing of a neuron and glial cells of a spinal cord smear.

Nervous and Muscular Tissues—Excitable Tissues

Excitability—ability to respond to stimuli by changingmembrane potential

Developed to highest degree in nervous and musculartissues

Membrane potential—electrical charge difference (voltage)that occurs across the cell membrane
In nerve cells, changes in voltage result in rapidtransmission of signals to other cells
In muscle cells, changes in voltage result in contraction,shortening of the cell

Nervous Tissue1

Communication byelectrical and chemicalsignals
Neurons (nerve cells)detect stimuli, transmitinformation rapidly toother cells
Neuroglia (glial cells)protect and assistneurons, are the“housekeepers” ofnervous system

https://alleninstitute.org/

Rethinking which cells are the conductors of learning and memory | Science News

Nervous Tissue2

Neuron

Neurosoma(cell body)—housesnucleus and other organelles;controls protein synthesis

Dendrites—short, branchedprocesses that receive signals fromother cells and transmit messagesto theneurosoma
Axon (nerve fiber)—sends outgoingsignals to other cells; can be morethan a meter long

What are the parts of the nervous system? | NICHD - Eunice Kennedy Shriver National Institute of Child Health and Human Development

Nih.gov; qbi.uq.edu.au

Muscular Tissue

Muscular tissue—elongated cells that are specialized tocontract in response to stimulation

Creates movements involved in body and limb movement,digestion, waste elimination, breathing, speech, and bloodcirculation

Important source of body heat

Three types of muscle: skeletal, cardiac, and smooth

Skeletal Muscle Tissue

Skeletal muscle

Made of muscle fibers—long thin cells
Most skeletal muscles attach to bone
Contains multiple nuclei adjacent to plasma membrane
Striations—alternating dark and light bands
Voluntary—conscious control over skeletal muscles

Figure 5.25

a:©Ed Reschke

Cardiac Muscle Tissue

Cardiac muscle

Limited to the heart wall
Cardiomyocytes are short and branched with one centrally locatednucleus
Intercalated discs join cardiomyocytes end to end

Provide electrical and mechanical connection

Striated and involuntary (not under conscious control)

Figure 5.26

a:©Ed Reschke

Smooth Muscle Tissue

Smooth muscle

Made of fusiform cells lacking striations

Cells are relatively short and have one central nucleus

Involuntary function
Most is visceral muscle—making up parts of walls of hollow organs

Figure 5.27

a:McGraw-Hill Education/DennisStrete, photographer

Tissue growth, development, degeneration, repair

Tissue Growth

Tissue growth—increasing the number of cells or size ofexisting cells

Hyperplasia—growth through cell multiplication

Hypertrophy—enlargement of preexisting cells

Muscle growth through exercise
Accumulation of body fat

Neoplasia—development of a tumor (neoplasm)

Benign or malignant
Composed of abnormal, nonfunctional tissue

Tissue Development

Tissues can change types within certain limits:

Differentiation= development of more specialized form andfunction by unspecialized tissue

Example: embryonic mesenchyme becoming cartilage and bone

Metaplasia= changing from one type of mature tissue toanother

Simple cuboidal tissue of vagina before puberty changes tostratified squamous after puberty
Pseudostratified columnar epithelium of bronchi of smokers tostratified squamous epithelium

Stem Cells1

Undifferentiated cells that are not yet performing anyspecialized function

Can differentiate into different types of mature cells

Image credit: Wikipedia

Embryonic stem cells

Totipotent: potential to develop into any type of fully differentiated human cell; from cells of very early embryo
Pluripotent: can develop into any type of cell in the embryo (but not accessory organs of pregnancy); from cells of inner cell mass ofembryo (blastocyst)

Adult stem cells—undifferentiated cells found in mature organs

Some are multipotent—able to develop into two or more cells (e.g., bone marrow stem cells)
Some are unipotent—produce only one cell type (e.g., cells giving rise to sperm)

Stem cells have diverse differentiation potential and may be classified as totipotent, pluripotent, multipotent or unipotent.

Image credit: Novus biologicals

Tissue Repair

Damaged tissues are naturally repaired in two ways:

Regeneration: replacement of dead or damaged cells bythe same type of cell as before

Restores normal function
Examples: repair of minor skin or liver injuries

Fibrosis: replacement of damaged cells with scar tissue

Scar holds organs together, but does not restore function
Examples: repair of severe cuts and burns, scarring of lungs intuberculosis

Tissue Degeneration and Death1

Atrophy—shrinkage of a tissue through loss in cell size ornumber; occurs in normal aging or lack of use

Necrosis—pathological tissue death due to trauma, toxins, orinfections

Infarction—sudden death of tissue when blood supply iscut off
Gangrene—tissue necrosis due to insufficient bloodsupply (usually involves infection)

Tissue Degeneration and Death2

Apoptosis—programmed cell death

Normal death of cells that have completed their function andbest serve the body by dying and getting out of the way
Phagocytized by macrophages and other cells
Billions of cells die by apoptosis
Every cell has a built-in “suicide program”